The present invention relates to particle beam writing using a Cell Projection system for fine image fabrication.
A particle beam writer uses one or more beams of particles to generate a given pattern on a plate. The plate is covered with a particle sensitive material. By way of example, consider the case of an Electron Beam Writing (EBW) technology. The EBW technology uses an electron beam to generate various patterns, by way of example, an integrated circuit pattern, on a substrate wafer.
A fundamental problem with the conventional optical lithography is the image quality degradation and the resolution limits caused by an optical proximity effect. One method to overcome this problem is an Electron Beam Direct Writing (EBDW) technology, a variation of the EBW technology. The theoretical resolution of an electron beam is finer, which allows writing denser layouts. The EBDW technology can be used for low-volume IC production at 90 nm and below. However, this technology has a lower throughput.
Several methods have been conventionally used to increase the throughput of IC fabrication. One such method is based on a Variable Shape Beam (VSB) technology, which facilitates writing patterns by using particle beam shots of fixed and simple shapes with variable size. By way of example, the simple shapes include rectangles and triangles. Further, the VSB-type EBW performs proximity effect correction by dose control, shape biasing and minute fracturing. However, such manipulations increase writing time.
Another conventional method used for IC fabrication is Cell Projection (CP) technology, which is also referred to as Character Projection or Block Projection. CP technology uses a stencil, which enables writing complicated repetitive patterns by one exposure shot. The throughput of a particle beam lithography system that writes circuits, measured in complete circuits written per unit of time, can be properly approximated by the number of exposures required to write the circuit. The number of exposures required to write the circuit is known as the shot count. A lower shot count results in a higher throughput and a higher shot count results in a lower throughput. By reducing the shot count, CP technology reduces the overall exposure time and increases the system throughput. However, the technique is limited by several restrictions pertaining to the geometric sizes and kind of figures that can be expressed. In addition, the proximity effect correction becomes a very challenging task.
In light of the foregoing discussion, a need exists for a method and system that improves the throughput of EBW technology and simultaneously maintains high accuracy using the CP system. Further, the system should be capable of effectively performing PEC, as well as providing the optimal design of the stencil. The present invention addresses such a need.